Utility Applications of Power Electronics
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Utility Applications of Power Electronics
• The applications of power electronics exist in many forms within the electric power system including: • High-Voltage Direct Current (HVDC) converter stations.
• Flexible AC Transmission System (FACTS) devices.
• The above systems are used to control and regulate AC power grids, to variable-speed drives for motors; interfaces with storage devices of several types, interfacing of distributed energy resources (DER) with the grid, electric drives in transportation systems, fault current–limiting devices, solid-state distribution transformers, and transfer switches.
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Required Power for Power Electronics
3
Typical Applications of Power Electronics Switches
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Switches for Power Electronics Thyristors
5
GTO and ICGT The GTO, makes it possible to build efficient converters for
output frequency control. The development of the GTO opened the way to high-power variable-speed ac motor drives and other
similar applications because a GTO, unlike a thyristor, can be turned off by injecting a large negative current to the gate. ICGT
represents an integrated gate drive unit.
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MOSFET
Power MOSFETs are unipolar, majority carrier, voltage-controlled devices, making them superior to bipolar devices (BJTs and IGBTs) in faster switching
speeds, lower switching losses, and simpler gate drives. The gate is composed of a silicon dioxide layer, called metal oxide, that normally insulates the
source from the drain. Once a forward-biased voltage is applied to the gate with respect to the source, the source becomes electrically conductive to the
drain, allowing the flow of appreciable currents.
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IGBT The IGBT is one of the most popular power electronic devices at
present. The IGBT combines the high-impedance, low-power gate input of a MOSFET with the power handling capacity of
bipolar transistors and thyristors. The MOS gate allows a high impedance control of the current flow through the device,
requiring extremely small amounts of power supplied to the control gate.
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Switches Comparison
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Thy
BJT
FET
GTO
IGBT
IGCT
Avail-
abilty Early
60s
Late 70s Early
80s
Mid 80s Late 80s Mid 90’s
State of
Tech. Mature Mature Mature/
improve
Mature Rapid
improve
Rapid
improvem
ent Voltage
ratings 5kV 1kV 500V 5kV 3.3kV 6.5kV
Current
ratings 4kA 400A 200A 5kA 1.2kA 4kA
Switch
Freq. na 5kHz 1MHz 2kHz 100kHz 1kHz
On-state
Voltage 2V 1-2V I* Rds
(on)
2-3V 2-3V 3V
Drive
Circuit Simple Difficult Very
simple
Very
difficult
Very
simple
Simple
Comm-ents Cannot
turn off
using gate
signals
Phasing
out in new
product
Good
performan
ce in high
freq.
King in
very high
power
Best
overall
performanc
e.
Replacing
GTO
Source: Dr. Zainal Salam, UTM-JB
Applications
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• For each of the following application, choose the best power switches and reason out why.
– An inverter for the light-rail train (LRT) locomotive operating from a DC supply of 750 V. The locomotive is rated at 150 kW. The induction motor is to run from standstill up to 200 Hz, with power switches frequencies up to 10 kHz.
– A switch-mode power supply (SMPS) for remote telecommunication equipment is to be developed. The input voltage is obtained from a photovoltaic array that produces a maximum output voltage of 100 V and a minimum current of 200 A. The switching frequency should be higher than 100 kHz.
– A HVDC transmission system transmitting power of 300 MW from one AC system to another ac system both operating at 50 Hz, and the DC link voltage operating at 2.0 kV.
Voltage and Current Requirements
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Importance
• Increasing applications of Power Electronic Equipment in Power Systems – Availability of high power
semiconductor devices – Decentralized renewable
energy generation sources – Increased power transfer
with existing transmission system
– Effective control of power flow needed in a deregulated environment
– Norms for Power quality
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Control Center
Micro-Turbine
Hospital
Commercial
Building
Fuel Cell
Smart House
Performance
Building
Combined Heat and Power
Plant (CHP)
Factory
Commercial Building
House
Apartment Building
Wind Power Plants
Village
Commercial
Building
Central Power
Station Solar Power Plants
CHP House
Future Power System
Function of Power Electronics in Utility Applications
• Enabling technology providing interface between two (ac/dc) electrical systems
• E.g. – Interconnection of two asynchronous ac systems. – DC to ac conversion is required to connect fuel cells or
photovoltaics to the utility grid.
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Converter
Controller
Source Load
Listing of Power Electronic Applications
• Distributed generation (DG) – Renewable resources (wind and photovoltaic) – Fuel cells and micro-turbines – Storage: batteries, super-conducting magnetic energy storage,
flywheels
• Power electronics loads: Adjustable speed drives • Power quality solutions
– Dual feeders – Uninterruptible power supplies – Dynamic voltage restorers
• Transmission and distribution (T&D) – High voltage dc (HVDC) and medium voltage dc – Flexible AC Transmission Systems (FACTS): Shunt and Series
compensation, and the unified power flow controller
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Power Device Capabilities and Resulting Power Electronic Structures
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IGBT MOSFET
Thyristor IGCT
101 102 103 104
102
104
106
108
Thyri
stor
IGBT
MOSFET
Po
wer
(V
A)
Switching Frequency (Hz)
IGCT
Structure of Power Electronic Systems
• Voltage-Link Systems – Transistors and diodes that
can block voltage of only one polarity
• Current-Link Systems – higher power bipolar voltage-
blocking capabilities of thyristors
• Solid State Switches
– bidirectional voltage blocking and current conduction
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AC1 AC2
AC1 AC2
Role of Power Electronics in Utility Applications
• Distributed Generation (DG) Applications Power electronic interface depends on the source characteristics
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(c)
AC
DC
DC
AC
Wound rotor
Induction Generator
Generator-side
Converter
Grid-side
Converter
Wind
Turbine
Isolated
DC-DC
Converter
PWM
Converter
Max. Power-
point Tracker
Utility
1f
Wind Power Generation with
Doubly Fed Induction Motors
Photo-voltaics Interface
Role of Power Electronics in Utility Applications
Power Electronic Loads: Adjustable Speed Drives
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(c)
Controller
Motor
Utility
Rectifier
Switch-mode
Converter
Role of Power Electronics in Utility Applications
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(c)
Load
Feeder 1
Feeder 2
Dual Feeders
Power Electronic
InterfaceLoad
Dynamic Voltage Restorers (DVR)
Uninterruptible Power Supplies
Rectifier Inverter FilterCritical
Load
Energy
Storage
Role of Power Electronics in Utility Applications
• Transmission and Distribution: DC Transmission
– most flexible solution for connection of two ac systems
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AC1 AC2
HVDC
AC1 AC2
MVDC
Role of Power Electronics in Utility Applications
• Transmission and Distribution: Flexible AC Transmission Systems (FACTS)
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1 2 sinE E
PX
1E
2E
3E
+- 3E1E 2E
Shunt
converter
Series
converter
I
Shunt and Series Compensation
Series Compensation
Shunt Compensation
Utility
STATCOM
jX
Discussion of Power Electronics Interface
• Fundamental concepts for understanding the operation of the power electronic structures
– voltage-link systems
– current link systems
– solid state switches
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Voltage-Link Systems
• Unifying approach: Power-Pole Building Block
– building block of all voltage-link systems
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AC1 AC2
dAi
Av
Ai
dV
controlv
1 or 0Aq
A sd T+
-
+
-
PWM
Voltage
port Current
port
Voltage-Link Systems
• Power conversion using Pulse Width Modulation (PWM)
– Power reversal with reversal of current direction
– Averaged conversion
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dAi
Av
Ai
dV
controlv
1 or 0Aq
A sd T+
-
+
-
PWM
Voltage
port Current
port
Av
t
dVAv
A sd T
sT
onA d A d
s
Tv V d V
T
Voltage-Link Systems • Averaged Representation of Power Pole
– Average quantities are of main interest
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dAi
Av
Ai
dV
controlv
A sd T+
-
+
-
PWM
1: Ad
dAi
Av
Ai
dV
controlv
1 or 0Aq
A sd T+
-
+
-
PWM
Voltag
e
port Current
port
( ) ( )A A dv t d t V
( ) ( ) ( )dA A Ai t d t i t
Voltage-Link Systems
• Synthesis of AC voltages: voltage to be synthesized; duty ratio needed; dc side current
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Ai
t0
v
dV
dV
2
0 t
Av
I
( ) sin2
dAN
Vv t V t
1sin
2Ad d t
1( ) sin ( )
2
1 ˆsin sin( )2
1 ˆ cos sin( ) cos(2 )2
dA ai t d t i t
d t I t
I d t d t
Voltage-Link Systems
• Implementation of bi-positional switch
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AidV+
-
Aq
Aq
1A Aq q
(d)
dAi
Av
Ai
dV
1 or 0Aq
A sd T+
-
+
-
Current-Link Systems
• Exclusively thyristor based
– One of (T1, T2, T3) and (T2, T4, T6) conduct at a time
– Average dc voltage controlled by ‘firing angle’
– Power flow reversed by reversing voltage polarity
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(d)
AC1 AC2
3 2 3cosd LL c dV V L I
ai
bi
cidv
+
-
dI
1T
3T
5T
4T
6T
2T
cL
bL
aL